1. Field of the Invention
The present invention relates to an discharge lamp lighting apparatus, a light source apparatus, a liquid crystal display (LCD) projector using a discharge lamp as a light source and the like, and more particularly to those where the lighting characteristic is much improved.
2. Description of the Related Art
In an LCD projector a discharge lamp is usually used as a light source for irradiating an LCD panel.
As widely known in the art, a discharge lamp is formed by enclosing high pressured gas into a tube shaped or valve shaped glass and light emission (lighting) is performed by applying a high voltage pulse (ignition voltage), ionizing the gas and supplying dive current thereto such that a continuous current conducts through the ionized gas.
In a discharge lamp lighting apparatus there is included a circuit (ignition circuit) for generating an ignition voltage and supplying it to the discharge lamp. In a conventional discharge lamp lighting apparatus, a fixed voltage level (voltage level which fits the watt power of the discharge lamp to be lighted) is generated as an ignition voltage and supplied to the discharge lamp.
FIG. 1 shows a typical constitution of an ignition circuit in a conventional discharge lamp lighting apparatus. A power supply line to which approximately 300V of DC voltage is supplied is grounded by means of a resistor R11 and a capacitor C11.
A connection midpoint between the resistor R11 and the capacitor C11 is connected to one terminal of a primary coil of a step-up transformer T11 by means of a discharge device H11 such as a SIDAC. The other terminal of the primary coil of the step-up transformer T11 is grounded.
One terminal of the secondary coil of the step-up transformer T11 is grounded and the other terminal thereof is connected to one terminal of a primary coil of a step-up transformer T12 by means of a diode D11 and a discharge gap H12. A connection midpoint between the diode D11 and the discharge gap H12 is grounded via a capacitor C12. The other terminal of the secondary coil of the step-up transformer T12 is grounded.
A discharge lamp 110 is attached to the lighting apparatus such that one of the electrodes thereof is connected to one terminal of the secondary coil of the step-up transformer T12.
Additionally a signal line for supplying an AC drive current from a full-bridge circuit (not shown) to the discharge lamp 110 is connected to the secondary coil of the step-up transformer T12.
According to this ignition circuit, approximately 300V of DC voltage from the power supply line is charged in the capacitor C11 through the resistor R11. When the charged voltage of the capacitor C11 attains to a discharge stat voltage of the discharge device H11, a voltage is supplied from the capacitor C11 to the primary side of the step-up transformer T11 and a stepped-up voltage obtained at the secondary side of the step-up transformer T11 is supplied to the capacitor C12 through the diode D11.
Then, when the charged voltage of the capacitor C12 attains to a discharge stat voltage of the discharge device H12, a voltage pulse is supplied from the capacitor C12 to the primary side of the step-up transformer T12 and a stepped-up voltage pulse obtained at the secondary side of the step-up transformer T12 is supplied to the discharge lamp 110 as an ignition voltage.
In this way an ignition voltage having a fixed voltage which is determined by the discharge stat voltage of the discharge device H12 is supplied to the discharge lamp 110.
However, supplying an ignition voltage having a fixed voltage to the discharge lamp has inconvenience mentioned below.
Namely, when an LCD projector is turned off after it is used for long hours and then the projector is soon or at once turned on again, the temperature of the discharge lamp is kept very high.
When the temperature of the discharge lamp is high in such a condition, the pressure of the low pressured gas which is enclosed in the glass of the discharge lamp increases, so that the discharge lamp cannot be lighted or turned on unless an ignition voltage of a higher voltage than that of normal temperature is supplied to the discharge lamp.
Accordingly, the discharge lamp cannot be lighted at a high temperature if the voltage level of the ignition voltage is fixed to a low voltage level which is sufficient for lighting the discharge lamp at a normal temperature. As a result when the LCD projector is turned off after it is used for long hours and then it is soon turned on again, the video image cannot be projected, so that users are inconveniently forced to wait until the temperature of the discharge lamp decreases.
On the other hand, if the voltage level of the ignition voltage is fixed to a high voltage level which is necessary for lighting the discharge lamp at the high temperature, a high voltage level of the ignition voltage is supplied unnecessarily at the normal temperature, so that the electrodes of the discharge lamp become deteriorated and it cases shortening of the life time of the discharge lamp.
In view of the aforesaid problem, the purpose of the present invention is to provide a lighting apparatus for an discharge lamp, a light source apparatus and a projection type display apparatus where the discharge lamp can be lighted or turned on also at a high temperature, the discharge lamp can be easily lighted regardless of the temperature and the life time thereof can be lengthened.
The present applicant proposes a discharge lamp lighting apparatus which comprises means for supplying a high voltage pulse (ignition voltage) to a discharge lamp, means for supplying a drive current to the discharge lamp, detecting means for detecting the temperature caused by the heat radiation of the discharge lamp, and control means for changing the voltage level of the ignition voltage in response to the detected result of the detecting means.
According to this discharge lamp lighting apparatus, the temperature caused by the heat radiation of the discharge lamp is detected by the detecting means and the voltage level of the ignition voltage is changed by the control means.
Accordingly, by changing the voltage level of the ignition voltage according to the temperature caused by the heat radiation of the discharge lamp, a high voltage level of the ignition voltage which is necessary for lighting the discharge lamp at a high temperature can be supplied to the discharge lamp when the discharge lamp is at a high temperature and on the other hand, a low voltage level of the ignition voltage which is sufficient for lighting the discharge lamp at a normal temperature can be supplied to the discharge lamp when the discharge lamp is at a normal temperature.
In this way the discharge lamp can be lighted or turned on when the discharge lamp is in its high temperature condition and at the same time it is avoided from supplying unnecessary high voltage level of the ignition voltage to the discharge lamp in its normal temperature condition, so that the deterioration degree of the electrodes of the discharge lamp becomes smaller and it causes lengthening of the life time of the discharge lamp.
In more detail for an example of this discharge lamp lighting apparatus, the discharge pulse supplying means includes a capacitor for charging a supplied voltage and a transformer for stepping-up the charged voltage of that capacitor; the control means is connected to a negative or positive thermistor; and a switching device for switching whether or not supplying a voltage from the capacitor to the transformer; wherein when the switching device is switched such that a voltage is supplied from the capacitor to the transformer, the voltage level of the charged voltage of the capacitor is made to change in accordance with the resistance value of the negative or positive thermistor where it is suitable to design that the negative or positive thermistor is used both for the aforesaid detecting means and the control means.
In view of the afore mentioned aspects, the voltage level of the ignition voltage can be changed in response to the temperature cased by the heat radiation of the discharge lamp only by adding a simple circuit such as a thermistor and a switching device.
Subsequently, the present applicant proposes a lighting apparatus which comprises a discharge lamp, means for supplying an ignition voltage to the discharge lamp, means for supplying a drive current to the discharge lamp, detecting means for detecting the temperature caused by the heat radiation of the discharge lamp, and control means for changing the voltage level of the ignition voltage in response to the detected result of the detecting means. In this example, the lighting apparatus means a combined one-body apparatus of the discharge lamp and the discharge lamp lighting apparatus.
According to this lighting apparatus, just same as the above mentioned discharge lamp lighting apparatus of the present invention, the discharge lamp can be lighted or turned on when the discharge lamp is at its high temperature condition and the life time of the discharge lamp will be lengthened.
Additionally the present applicant proposes a projection type display apparatus using a discharge lamp as a light source which comprises means for supplying an ignition voltage to the discharge lamp, means for supplying a drive current to the discharge lamp, detecting means for detecting the temperature caused by the heat radiation of the discharge lamp, and control means for changing the voltage level of the ignition voltage in response to the detected result of the detecting means.
According to this projection type display apparatus, just same as the above mentioned discharge lamp lighting apparatus of the present invention, the discharge lamp can be lighted or turned on even when the discharge lamp is at its high temperature condition. Accordingly, when the projection type display apparatus is turned off after it is used for long hours and then it is soon turned on again, the video image can be projected at once, so that it becomes easy for users to handle the projection type display apparatus. At the same time the life time of the discharge lamp will be lengthened.